This invention relates generally to the field of radiation detector assemblies and more particularly to the detector assemblies having coatings for improved longevity. Such radiation detector assemblies are particularly suitable for use in digital X-ray detector assemblies such as those used in medical or industrial inspection applications.
In an X-ray detector assembly, an amorphous silicon detector substrate is coated with a vapor phase deposited X-ray scintillator material. The scintillator material generates photons isotropically from the absorption of the X-rays. A reflective layer is required above the scintillator layer to reflect photons, which are emitted in a direction away from the detector substrate, back towards the detector substrate.
One important factor in medical imaging applications is the detector spatial resolution. Photons, which are generated in the scintillator material over one detector pixel, must be counted only by that underlying pixel to obtain a high image resolution. Photons that are scattered to adjacent pixels reduce the clarity of the image. To reduce photon scatter, the scintillator material is vapor deposited in columnar or needle form. Individual needles are separated from one another and they possess aspect ratios (length/diameter) of 100 or greater. Photons traveling down the scintillator needles tend to be contained within the individual needle due to the higher refractive index of scintillator material over air, provided that the individual scintillator needles remain separated. The Cesium Iodide (CsI) scintillator material is known to be a very hydroscopic salt. Exposure of the CsI scintillator material to moisture can cause the CsI scintillator material to absorb the moisture, which further causes the individual CsI scintillator needles to coalesce, thereby reducing the detector image quality.